γ-Aminobutyric acid, or GABA, is the chief inhibitory neurotransmitter in the developmentally mature mammalian central nervous system. Its principal role is reducing neuronal excitability throughout the nervous system.
An imidazopyridine is a nitrogen containing heterocycle that is also a class of drugs that contain this same chemical substructure. In general, they are GABAA receptor agonists, however recently proton pump inhibitors, aromatase inhibitors, NSAIDs and other classes of drugs in this class have been developed as well. Despite usually being similar to them in effect, they are not chemically related to benzodiazepines. As such, GABAA-agonizing imidazopyridines, pyrazolopyrimidines, and cyclopyrrones are sometimes grouped together and referred to as "nonbenzodiazepines." Imidazopyridines include:
The GABA receptors are a class of receptors that respond to the neurotransmitter gamma-aminobutyric acid (GABA), the chief inhibitory compound in the mature vertebrate central nervous system. There are two classes of GABA receptors: GABAA and GABAB. GABAA receptors are ligand-gated ion channels ; whereas GABAB receptors are G protein-coupled receptors, also called metabotropic receptors.
The GABAA receptor (GABAAR) is an ionotropic receptor and ligand-gated ion channel. Its endogenous ligand is γ-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system. Accurate regulation of GABAergic transmission through appropriate developmental processes, specificity to neural cell types, and responsiveness to activity is crucial for the proper functioning of nearly all aspects of the central nervous system (CNS). Upon opening, the GABAA receptor on the postsynaptic cell is selectively permeable to chloride ions (Cl−) and, to a lesser extent, bicarbonate ions (HCO3−).
GABAB receptors (GABABR) are G-protein coupled receptors for gamma-aminobutyric acid (GABA), therefore making them metabotropic receptors, that are linked via G-proteins to potassium channels. The changing potassium concentrations hyperpolarize the cell at the end of an action potential. The reversal potential of the GABAB-mediated IPSP is –100 mV, which is much more hyperpolarized than the GABAA IPSP. GABAB receptors are found in the central nervous system and the autonomic division of the peripheral nervous system.
The GABAA-rho receptor is a subclass of GABAA receptors composed entirely of rho (ρ) subunits. GABAA receptors including those of the ρ-subclass are ligand-gated ion channels responsible for mediating the effects of gamma-amino butyric acid (GABA), the major inhibitory neurotransmitter in the brain. The GABAA-ρ receptor, like other GABAA receptors, is expressed in many areas of the brain, but in contrast to other GABAA receptors, the GABAA-ρ receptor has especially high expression in the retina.
Allopregnanolone is a naturally occurring neurosteroid which is made in the body from the hormone progesterone. As a medication, allopregnanolone is referred to as brexanolone, sold under the brand name Zulresso, and used to treat postpartum depression. It is given by injection into a vein.
A GABA receptor agonist is a drug that is an agonist for one or more of the GABA receptors, producing typically sedative effects, and may also cause other effects such as anxiolytic, anticonvulsant, and muscle relaxant effects. There are three receptors of the gamma-aminobutyric acid. The two receptors GABA-α and GABA-ρ are ion channels that are permeable to chloride ions which reduces neuronal excitability. The GABA-β receptor belongs to the class of G-Protein coupled receptors that inhibit adenylyl cyclase, therefore leading to decreased cyclic adenosine monophosphate (cAMP). GABA-α and GABA-ρ receptors produce sedative and hypnotic effects and have anti-convulsion properties. GABA-β receptors also produce sedative effects. Furthermore, they lead to changes in gene transcription.
L-838,417 is an anxiolytic drug used in scientific research. It has similar effects to benzodiazepine drugs, but is structurally distinct and so is classed as a nonbenzodiazepine anxiolytic. The compound was developed by Merck, Sharp and Dohme.
SL651498 is an anxiolytic and anticonvulsant drug used in scientific research, with a chemical structure most closely related to β-carboline derivatives such as abecarnil and gedocarnil. It has similar effects to benzodiazepine drugs, but is structurally distinct and so is classed as a nonbenzodiazepine anxiolytic.
Gamma-aminobutyric acid receptor subunit alpha-3 is a protein that in humans is encoded by the GABRA3 gene.
Gamma-aminobutyric acid receptor subunit alpha-2 is a protein in humans that is encoded by the GABRA2 gene.
TPA-023 (MK-0777) is an anxiolytic drug with a novel chemical structure, which is used in scientific research. It has similar effects to benzodiazepine drugs, but is structurally distinct and so is classed as a nonbenzodiazepine anxiolytic. It is a mixed, subtype-selective ligand of the benzodiazepine site of α1, α2, α3, and α5-containing GABAA receptors, where it acts as a partial agonist at benzodiazepine sites of the α2 and α3-containing subtypes, but as a silent antagonist at α1 and α5-containing subtypes. It has primarily anxiolytic and anticonvulsant effects in animal tests, but with no sedative effects even at 50 times the effective anxiolytic dose.
L-655,708 (FG-8094) is a nootropic drug invented in 1996 by a team working for Merck, Sharp and Dohme, that was the first compound developed which acts as a subtype-selective inverse agonist at the α5 subtype of the benzodiazepine binding site on the GABAA receptor. It acts as an inverse agonist at the α1, α2, α3 and α5 subtypes, but with much higher affinity for α5, and unlike newer α5 inverse agonists such as α5IA, L-655,708 exerts its subtype selectivity purely via higher binding affinity for this receptor subtype, with its efficacy as an inverse agonist being around the same at all the subtypes it binds to.
CGP-7930 was the first positive allosteric modulator of GABAB receptors described in literature. CGP7930 is also a GABAA receptor positive allosteric modulator and a blocker of Potassium channels.
DS-1 is a drug from the imidazopyridine family, which is the first drug developed that acts as a GABAA receptor positive allosteric modulator (PAM) selective for the α4β3δ subtype, which is not targeted by other GABAA receptor PAMs such as the benzodiazepines or other nonbenzodiazepine drugs. Novel selective drugs such as DS-1 are useful in the study of this receptor subtype.
A phosphodiesterase-4 inhibitor, commonly referred to as a PDE4 inhibitor, is a drug used to block the degradative action of phosphodiesterase 4 (PDE4) on cyclic adenosine monophosphate (cAMP). It is a member of the larger family of PDE inhibitors. The PDE4 family of enzymes are the most prevalent PDE in immune cells. They are predominantly responsible for hydrolyzing cAMP within both immune cells and cells in the central nervous system.
Cartazolate (SQ-65,396) is a drug of the pyrazolopyridine class. It acts as a GABAA receptor positive allosteric modulator at the barbiturate binding site of the complex and has anxiolytic effects in animals. It is also known to act as an adenosine antagonist at the A1 and A2 subtypes and as a phosphodiesterase inhibitor. Cartazolate was tested in human clinical trials and was found to be efficacious for anxiety but was never marketed. It was developed by a team at E.R. Squibb and Sons in the 1970s.
NS-11394 is a drug which acts as a subtype-selective positive allosteric modulator at GABAA receptors, with selectivity for the α3 and α5 subtypes. It has been researched as an analgesic for use in chronic or neuropathic pain.
A GABA analogue is a compound which is an analogue or derivative of the neurotransmitter gamma-Aminobutyric acid (GABA).
